Separation of immiscible phases, oil and water in particular, has many uses. Such separation can be used in collection of desirable oils, and cleaning of waste water. Early methods included letting the phases separate by gravity and/or cooling until solidification occurred then removing the solids. However, solidification is not practical for light oils, and phase separation based only on gravity takes time. A problem with phase separation occurs when the oil forms very small droplets which tend to disperse throughout the aqueous phase. Overcoming surface tension to get small droplets to merge is coalescing. Larger droplets coalesce better than small droplets making separation of the phases then possible. However, getting the fine droplets to coalesce has been difficult and time consuming.
U.S. Pat. No. 4,802,978 discloses an inclined plate separator of a kind commonly used to coalesce and separate oil droplets dispersed in an aqueous liquid. This separator uses a series of corrugated oleophilic plates arranged in a cylindrical tank to one side of a diffusion baffle. The plates are inclined upward to take advantage of gravity. However, for some systems, a secondary separator, which uses oleophilic filtering material, is necessary because the inclined plate separator alone cannot completely coalesce and separate the oil droplets.
U.S. Pat. No. 4,385,986 discloses a gravity separator also having slanted separator plates for separating bilge water.
U.S. Pat. No. 4,859,329 describes a system for separating oils from waste wash water in which "Mechanically emulsified oil products are coalesced using a matrix of polypropylene baffles". Such baffles are described as effective in coalescing globules down to 20 microns. However, a disadvantage of polypropylene attraction noted by the patent is that it will not remove light or emulsified oil and will not work in heavy flows.
U.S. Pat. No. 4,643,834 discloses a multiple stage coalescer having inclined V shaped plates with progressively finer clearances between plates from stage to stage. The patent states "Where turbulence is avoided, flocculations and coalescence--and hence separation--all take place more efficiently."
U.S. Pat. No. 3,800,945 discloses a cell claiming catalytic action for coalescing oil droplets. Catalytic agents are impregnated into emulsion breaking fibrous material which is wound around a core.
U.S. Pat. No. 3,563,389 discloses a gravitational settler adapted for separation of liquid-liquid dispersions. A series of sloping plates are used to increase the rate of coalescence of droplets. Suitable distance between the plates is suggested to be 5 to 60 mm, preferably 10 to 40 mm.
Disk filters are well known for high flow rate filtration of particulates from liquids, particularly water used in drip irrigation systems. However, the inventor is unaware of the use of such filter disks as components in oil/water separation systems.
U.S. Pat. No. 5,098,565, incorporated herein by reference, discloses a stacked disk-type filter designed to fit in a standardized housing. The disks have fingers which permit particulate matter to become disengaged.
U.S. Pat. No. 4,880,537, incorporated herein by reference, discloses a stacked disk type filters having a variety of spacing arrangements, for example, defining grooves on a first surface and accumulator grooves on a second surface.
U.S. Pat. No. 4,592,839, incorporated herein by reference, discloses a multiple disc filter for removal of particulate matter from water. Such disk filters are commonly used in drip irrigation systems.
Inclined plate separators and other types of existing coalescer-separator systems available till the present invention have the following disadvantages: low throughput to avoid turbulence, long residence time and therefore large holdup volume, and relatively low separation efficiency for small droplet dispersions.